The atrial trabeculae of frog heart may be dissected free of the atrial wall relatively easily. Most range from 25 to 100 micron m in diameter and up to seven mm long. It has been shown that the time courses of currents passed during attempted voltage clamps experiments may be simulated with modest success using a simple geometrical model. The model assumes for the sodium current that Hodgkin-Huxley membrane regions are connected radially through external resistances dependent on the radial depth of the region. Comparisons of digital simulations of the behavior of our equivalent circuits for the sodium current with the results of voltage controlling experiments will be made. In this way we will test the applicability of H-H equations and other ion conductance formalisms to frog heart trabeculae. Similar methods will be used to extend our analysis to the slow inward current. The frog heart is also a favorable object for the biochemical analysis of an excitable membrane. We will continue our purification of plasma membranes and the solubilization of the membrane proteins. Proteins, free of membrane but not phospholipid (or detergent), will be electrophoresed in acrylamide gels for separation, identification and characterization. Radioactive TTX will be used to identify any TTX binding components of the solubilized membrane protein population. The binding kinetics will be determined. Recombination experiments will be pursued with the eventual goal of establishing sodium channels in artificial membranes. Finally antibodies are available which will be used to analyse protein-lipid interactions.